For mine, it seemed like old messages when messages and chat were separate.
I DEFINITELY always fact check these type of things. Like I said, I ignored it the first couple times and was even in the process of telling someone they were wrong about it when I decided to look and was shocked.
I can not 100% positively say they were private messages....but they were things I know the person posting would not want to be public on my wall so its still worth checking.